Retarding the diffusion rate of piperazine through the interface of aqueous/organic phase: Bis-tris propane tuned the trans-state of ultra-low concentration piperazine

An urgent challenge during the preparation of polyamide thin film composite membrane via the interfacial polymerization method was excessive diffusion rate of piperazine to form uncontrollable polyamide layer thickness, ultimately leaded to low water permeability to increase the operating cost. Herein, a uniquely new method, which brought down one order of magnitude of piperazine concentration to ultra-low grade (0.01% w·v⁻¹) to retard the diffusion rate, was utilized to avoid the problem. However, the ultra-low concentration of piperazine could not easily react with trimesoyl chloride, bis-tris propane as conditioning agent was needed to overcame the trouble. The kinetics diffusion process of piperazine under the function of bis-tris propane was intensively studied by molecular dynamics simulation and other characterizations. Bis-tris propane could combine with piperazine to generate intermolecular force and then carry piperazine molecules moving toward the interface of aqueous/organic phase, which tuned the trans-state of piperazine to the benefit of rection. This work offered a novelty insight to surmount the problem of the excessive diffusion rate, which could promote the development of membrane technology.